Process for sealing receptacles



J. H PAYNE 2 1413323 PROCESS FOR SEALING RECEPTACLES Original FiledApril 28, 1936 is Attov'neg.

Patented Dee. 27, 1938 PROCESS FOR SEALING RECEPTACLES John H. Payne,Ballston Spa, N. Y., assl'gnor to General Electric Company, a

New York corporation of Original application April as, 1936, Serial No.76,796, now Patent No. 2,101,156, dated December '7, 1937.

Divided and this application November 27, 1936, Serial No. 112,884

' 3 Claims. (Cl. 219-10), I

This application is a division of my prior al plication, Serial No.76,796,'filed April 28, 1936 (now Patent No. 2,101,156, granted Dec. '7,1937). The invention described and claimed herein re-.

5 lates to the art of sealing hollow metallic receptacles, and moreparticularly to a process for use in this art.

Although not limited thereto, the invention has been found to havespecial utility in the manufacture of electric switches of the liquidcontact variety such as are described, for example, in my copendingapplication, Serial No. 759,527, filed December 28, 1934 (now Patent No.2,101,092, granted Dec. 7, 1937). The switches therein disclosedtypically comprise a closed vessel consistins of a pair of dished wallmembers of thin metal separated and insulated from one another by anapertured disk of non-conducting material. a body of mercury beingarranged within thevessel to make and break an electrical circuitbetween the wall members. It is generally found desirable to provide anoperating atmosphere of a reducing gas, such as hydrogen, which may beintroduced into the vessel through a small aperture which is thereaftersealed off. d

In order to assure long life and reliable operation of such switches, itis essential that the enclosing receptacle be sealed in such a way as toremain entirely gas-tight under all conditions of use. Seals of readilyfusible materials, such as solder, have been found to be unsatisfactoryfor this purpose because of the impossibility of causing them to uniteintegrally with the metal of the switch. Furthermore, the low meltingpoint metals now available are attacked by mercury in such a way as torender them unsuit'able for this use. Y

* On the other hand, due to the thinness of the wall material requiredby considerations of econ omy to be used in switch manufacture, it hasheretofore proved impracticable to produce a satisfactory seal bywelding with high melting point materials. At low welding currents themechani-- cal pressure required to secure'proper joining of the parts issogreat as'to cause bending of the switch receptacle, while at highercurrents there is a strong tendency to burn the metal and to produce aleaky seal.

It is an object of the present invention to provide a method of sealingan aperture in a thin metal receptacle by welding a' body of'difiicultly fusible metal into the aperture in such a way as cation ofthe invention comprises the steps of po- Tsitioning a. slug of dimcultlyfusible metal in a receptacle aperture to be sealed so that a relativelyextensive contact area exists between the receptacle and the slug, andfusing the slug by welding current entering through a very small areathereof remote from the receptacle.

The novel features whichI believe to be characteristic of my inventionare set forth with particularity in the appended claims. My inventionitself, however, both as to its organization and the method ofoperation, together with further objects and advantages thereof, willbest be undertaken in connection with the accompany drawing, in whichFig. 1 ls a view in partial section of a liquid contact switch containerof a type to which the invention is particularly applicable; Figs. 2, 3,4 and 5 illustrate successive steps in the practice of the invention,and Fig. 6 is a fragmentary sectional view showing an alternative modeof application of my invention.

The nature of my invention may best be understood by considering itsapplication to a particular use such as sealing -a liquid contact switchreceptacle. of the type illustrated in Fig. l. The

receptacle there shown comprises a pair of dished thin metal wallmembers i0 and ii positioned on --cept forthe provision in one of thewall members of a small aperture i6. This is used in the final stages ofmanufacture to introduce into the (designated by the dotted line ll),which is needed for contact making operations and to permit theestablishment of a desired gas pressure inside the switch during thesealing process. In accordance'with the present invention the apertureI6 is located at the bottom of a depression formed byan inwardly bentportion i8 of the receptacle wall. As will be pointed out more fully inthe following this, configuration is extremely useful in positioning theclosure elements employed intthe sealing operation.

- In 'order' finally to seal the switch receptacle stood by reference tothe following specification I otherwise closed receptacle a quantity oimercury invention it is preferred to form the closure element of adifficulty fusible metal 'having a melting point on the order of that ofthe switch material and capable of being integrally welded to the same.Metals which are particularly suitable for this use include steel,chrome-iron alloys and nickel, all of which are substantially resistantto mercury corrosion. Where steel balls of the type commerciallyavailable for ball bearings are to be employed, it is advantageous tosoften them somewhat by decarbonizing them in hydrogen or in a similarreducing atmosphere.

With the switch parts in the position indicated the spherical closureelement is necessarily caused to cometo rest at the proper place as aresult of the inwardly directed slope of the depressed wall portion I8.Consequently, automatic feeding of these elements is entirely practical.It will be understood, of course, that each element should be ofslightly larger diameter than theaperture It in order to prevent itsfalling to the switch container.

In order to weld the closure element into place a welding assembly ofthe type illustrated may be employed. This assembly may, for example,form a part of the sealing machine described in my aforementioned priorapplication, Serial No. 76,796. As shown, a stationary hollow electrode2| is placed in contact with the outer surface of the wall member l0,being shaped if desired to correspond with the slope of the depressedwall portion l8. In order to render the joint between the electrode andthe wall member substantially gas-tight a gasket 22 is provided whichseats firmly against the surface of the wall member. As a result of thisgas-tight connection a desired condition of gas pressure or vacuum maybe established within the receptacle before it is sealed, such pressurebeing communicated through the. hollow electrode 2|. In the manufactureof switches of the type under consideration the sealing operation willpreferably take place when the switch receptacle and the interior of theelectrode are subjected to hydrogen at a pressure of .the order of from1 to 2 atmospheres. In order to permit closure elements to be fed intoplace after the desired gas pressure is created, a hollow tube 24 isprovided which passes laterally through the electrode 21 and the gasket22.

Cooperating with the stationary electrode 2| there is provided a movableelectrode 2! arranged concentrically within the former. Referring toFig. 3 it will be seen that the lower surface of this electrode isflattened and is adapted to, contact the closure element IO. It is alsocontemplated that during the welding operation the contact pressurebetweenthese two elements shall be very slight, being provided, forexample, by the weight of the movable electrode only or by the weight ofthe electrode assisted by a weak compression spring. Under theseconditions the initial area of contact between the electrode and theclosure member will be extremely small, closely. approximating a pointcontact. On the other hand, since the diameter of the sphere ll is butslightly greater than that of the aperture It a relatively extensivecontact area for the passage of welding current exists between thewelding operation is complete.

-.WhileIhave'describedmy sphere and the receptacle wall. For thisreason, when an impulse of high amperage welding current is passedserially through the electrode 2!, the closure element II, and thereceptacle wall portion ll (whence it returns to the cooperating weldingelectrode 2!), intense heating of the closure member is produced at itsupper portion with a minimum of heating at the portion in contact withthe receptacle wall. As a result local fusion occurs at the top of thesphere causing the same to develop a mushroom portion 21 which flowsoutwardly over the coolerlower portion. Ihis latter remains in arelatively unfused condition but is sumciently hot to be forced downinto the aperture l6, becoming integrally united with the walls of thesame during the last instant that the welding current is permitted toflow. 80 little welding pressure is required by this process thatbending of the thin metal of the receptacle wall is effectively avoided.

In Fig. 5 I have illustrated the electrode andswitch assembly as itappears at the instant the At this time the aperture i8 is hermeticallyclosed by the fused member I! which now comprises a portion projectinginto the aperture and an upper enlargement which overlaps the edges ofthe aperture and is integrally united with the outer surface of thereceptacle.

The foregoing mode of procedure has been found to result in asurprisingly small number of imperfect seals due to the fact that themetal of the closure element has a high melting point and by the weldingprocess is integrally united with the metal surrounding the aperture.The closure is inherently gas-tight and, since the sealing materialpreferably comprises a metal which is not attacked by mercury, gradualcorrosion of the seal no longer constitutes a limitation on the life ofthe switch.

invention as being preferably applied in connection with a sphericalclosure member, it is not necessarily limited thereto. In Fig. 6 I haveillustrated an alternative application in which the closure element 28is of essentially rhombic cross-section having one apex sealed in theseal-oi! aperture I. and the other in a relatively small opening IIprovided for that purpose in the lower face of a welding'electrode'll.It will be understood that due to the slight contact existing betweenthe electrode Hand the slug 2! the initial fusion will be substantiallylocalized at the upper part of the slug thus causing the desiredmushrooming effect described in connection with Fig. 4. 1

In the appended claims L'aim' to cover this and all other modificationswhich fall within the true spirit and scope of the foregoing disclosure.What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

-"1. The process of sealing an-aperture inan exposed surface of athinmetal body under circumstances which prevent applying a reinforc-.

point contact with the member at a region thereof remote from the body,passing an electric current serially through the electrode, the memberandthebodysuflicienttoinitiatefusion ofthe member at its point ofcontact with the electrode, and continuing such current without theapplication of appreciable electrode pressure to cause progressive flowof metal from the region of electrode contact into welding relation withthe exposed surface of the body around the aperture and to producepartial penetration of the member into the aperture, thereby completelyto close the same.

2. The process of hermetically, sealing an aperture in a receptacleconstituted of such thin metal as to be readily deformable, whichprocess comprises positioning in the aperture and in direct contact withthe metal of the receptacle a generally spherical member consisting of a.metal which is adapted to weld integrallyto' the metal of thereceptacle, the member being of such dimensions as to be incapable ofpassing through the aperture, bringing a welding electrode into lightpressure contact with the member at a region thereof remote from thereceptacle, passing an electric current serially through the electrode,the member and the receptacle to initiate fusion or the member at theregion of its contact with the electrode, and continuing such currentwithout the application oi. substantial electrode pressure to 'causeprogressive flow of metal from said region into welding relation withthe outer surface of the receptacle around the aperture thereby toeffect complete closure of the aperture.

3. The process of sealing an aperture in a thin metal receptacle whichcomprises providing a de- 1 pression in one face of said receptacle,iorming a circular aperture at the bottom oi the depression, positioningin said aperture a spherical metal member of such dimensions as to seatreadily therein in contact with the metal of the receptacle, bringing anelectrode surface into light pressure point contact with the member at aspot remote from the aperture, passing an electric current seriallythrough the electrode, the member and the wall of the receptaclesufflcient to initiate fusion of the member at its point of contact withthe electrode and continuing such current without the application ofappreciable electrode pressure to cause progressive flow of metal fromthe region of electrode'contact into welding relation with the outersurface of the receptacle around the aperture and to produce partialpenetration of the member into the aperture.

JOHN H. PAYNE.

